FORT THOMAS  Until she was almost home and was closing her Nissan Sentra's power windows, Sharon Everett probably never smelled the combustible gases that had built up in her car.

But it could have been only a few seconds before the fumes, heated by summer and mixed with a household product, set off a flash fire that critically injured the Fort Thomas woman.

Investigators say this is their working theory about the Sunday afternoon fire; they are awaiting lab results to be sure.

In the meantime, some experts are sounding an alarm, warning that pool chemicals in certain conditions can be deadly.

When you are mixing some of these chemicals, you can get a rather dramatic chemical reaction, said Max West, sales manager for Eastgate Pools in Mount Carmel.

Some of the most common pool chemicals are gaseous products. They will heat and expand. And the result could be catastrophic if not handled properly.

Ms. Everett, 51, is in critical condition at University Hospital, suffering from third-degree burns over 56 percent of her body.

She had been returning home from a trip to the grocery when fire started behind her driver's seat on the floorboard, where she had put her groceries. Investigators believe she had driven with her windows open because her air conditioning wasn't working, but had closed them as she neared home.

State Fire Marshal Jack Flowers and Fort Thomas Fire Chief Dale Edmondson said they would not identify the products or the pool chemical until lab tests confirm their findings.

One of the most common pool chemicals, chlorine, is sometimes made with calcium hypochlorite, a substance that is suspected by the British Maritime and Coast Guard agency to have caused explosions and fires in the hulls of ships transporting the chemical in recent years.

The maritime agency in November issued an advisory.

Calcium hypochlorite, hydrated is suspected as being a factor in these fires; however this has not been proven.

The fires occurred in tropical waters, the agency said, and were characterized by an explosion and an intense fire fed by the ready availability of oxygen.

Consumers should follow these safety procedures, said Mr. West.

 Read product labels and ask the salesperson to clear up any unanswered questions.

 Keep pool chemicals separate from other household items.

 Keep pool chemicals in dry, cool storage areas.

 Don't store pool chemicals in car garages.

 Don't leave pool chemicals in a car for long periods of time, especially on hot days.